This invention relates to a tube for medical applications and to an extracorporeal circuit for blood circulation.
In particular this invention relates to a tube for medical applications used to construct the extracorporeal circuit of a machine for the purification of blood.
Moreover the invention relates to an extracorporeal circuit for blood circulation of a machine for blood purification, to which the present invention will make specific reference without thereby relinquishing its general applicability.
A known machine for the purification of blood comprises an extracorporeal blood circuit and a blood processing unit, commonly known as a filter, which comprises a compartment through which blood passes when in use and a compartment to receive the undesired substances contained in the blood. The two compartments of the filter are separated by a semipermeable membrane.
An extracorporeal blood circuit comprises, in addition to the venous branch and the arterial branch, connectors for the needles, connectors for sensors, a casing forming two expansion chambers, and various branches connected to the expansion chamber. In practice, each extracorporeal circuit comprises first components made from flexible material, such as the tubes that form the arterial branch and the venous branch, and second components made from rigid material such as the connectors and the casing.
The materials chosen for making the first and second components are generally polymers, which must have specified general characteristics, such as transparency and mechanical strength. In addition, the materials used for making the tubes must have a specified elasticity and a specified resistance to kinking, in other words the capacity to prevent the blocking of the tube when the tube is bent around one point of the tube itself.
PVC has all the abovementioned characteristics and is therefore generally used for making the tubes.
Although PVC has the undoubted advantages cited above, it also has drawbacks associated with the disposal of the extracorporeal circuit. For example, the first and second components of the extracorporeal circuit come into contact with the blood during the blood treatment, and must be incinerated. The incineration of PVC causes the emission of substances that are harmful both to the environment and to the human body. The substances emitted during incineration include particularly harmful ones such as hydrochloric acid (HCl), polychlorinated dibenzodioxins, and furan toxins.
Another disadvantage of the use of PVC relates to the presence of di(2-ethylhexyl)phthalate (DEHP), which is used as a plasticizer in combination with the PVC and is suspected of acting as a carcinogen.
Since it became a requirement to avoid polymers containing chlorine, various chlorine-free polymers with similar physical and mechanical characteristics to PVC have been proposed. However, these chlorine-free polymers have a number of disadvantages arising from the operations of joining the different components of the extracorporeal circuit.
In particular, these disadvantages arise from the fact that, in general, the joining operations are carried out by applying either thermal energy or radio-frequency energy to the parts included in the joints. As a result of the heat that they inevitably produce, these joining procedures can seriously damage the tubes, to such an extent that their function is adversely affected. This is because the heat required for welding is frequently considerable, since the first and second components must withstand without degradation the high sterilization temperatures required by the regulations concerning material for biomedical use. Consequently, the application of a large quantity of heat, sufficient for effective welding, to small components cannot be easily controlled.